The present invention is directed to a liquid transfer device wherein a plurality of pipette-type devices can simultaneously pick up predetermined quantities of liquid from a suitable source and dispense the same into a plurality of individual receptacles.
Many tests and applications in the medical field require picking up predetermined amounts of liquid reagents from one container and injecting or depositing the same into another receptable or container as a daily or routine testing procedure. An example of such a test is one performed in a multi-well microtube tray where a culturing/rehydrating medium is added to a dried prepared microtube tray to perform an antibiotic sensitivity test or bacterial identification.
In the past, pins or prongs such as disclosed in the U.S. Pat. No. 2,956,931, to Goldberg, or loops as disclosed in the U.S. Pat. No. 4,115,200, to Anderson, were used for picking up small drops by surface tension and depositing them in another solution. The amount of liquid transferred by such means is generally limited and such means basically carry on a mixing operation because they take out the same volume they put in. The risk of contamination is high due to the contact of the prong or loop with the various mixtures in the containers. These drawbacks can be overcome by a positive displacement device such as a syringe. However, syringes generally require the use of O-rings or other close tolerance type seals which provide restraint to movement making them hard to operate when grouped into a multiple syringe device. Furthermore, use of such syringes is apt to be trouble prone as they can be easily contaminated, expensive or bulky.
The U.S. Pat. No. 3,982,438, to Byrd, discloses a multiple channel pipetting apparatus wherein a plurality of small tubes extend downwardly with the upper end portions communicating with reservoirs that have a predetermined volume. A flexible diaphragm extends across all of the reservoirs and the upper portions thereof are in communication with a common manifold chamber. The application of positive or negative pressure moves the diaphragm downwardly and upwardly into contact with the lower and upper reservoir walls respectively to either expel liquid from or draw liquid into the tubes. The accuracy of the amounts of liquid extracted or expelled by the tubes is dependent upon the pressure in the manifold chamber and the volume thereof and does not rely upon the use of reciprocating plungers.
The U.S. Pat. No. 3,568,735, to Lancaster, discloses a laboratory microtitration dispensing apparatus comprising a manifold connected to a plurality of passageways, a head member connected to the manifold and having a plurality of apertures aligned with the passageways but separated therefrom by a flexible diaphragm, an actuator mounted in each aperture including a piston normally biased by a spring to maintain the flexible diaphragm means out of its respective one of said apertures and a dispensing needle connected to each actuator assembly whereby, upon supplying and exhausting air to and from the manifold, the diaphragm will be moved by the differential pressure on opposite sides thereof to operate the pistons in the respective apertures to control the pick up and discharge of fluid by the needles. Thus, Lancaster utilizes air pressure in the manifold for controlling the transfer of liquid as does the patent to Byrd.
The U.S. Pat. No. 4,047,438, to Sekine, discloses a liquid quantitative dispensing apparatus for withdrawing liquid into a plurality of pipettes arranged in rows by simultaneously pressing and releasing cap-like projections formed of flexible material and dispensing the liquid to test tubes and the like. The cap-like projections of flexible material are disposed in alignment with a plurality of pipettes and extend upwardly into bores in a guide plate. A plurality of plungers secured to a common plate are operative within the bores for pressing on the cap-like projections to dispense liquid from the pipettes. In this patent, as well as the two previously mentioned patents, it is extremely difficult to provide a good seal for the membrane since the membrane is being clamped between two flat surfaces.